I don't know the answer to your question. But since there is no official Staff support for the CSS upgrade, and precious little Volunteer support, I recommend you go to Appearance > Edit CSS. That's where as wordpress has provided a preview function you can use while you wait for a Volunteer with CSS editing experience to help you.

The method below isn't particularly pretty, especially when the font size is increased or the browswer window is compressed but I can't think of a better way at the moment. You might want to change the position values slightly to taste but it should work OK.